This invention relates to a polarization key for use with an electrical connector such as a circuit board edge connector.
In a typical electronic assembly, a number of circuit boards containing various circuits each plug into a separate multi-contact connector mounted on a backplane board. The backplane board interconnects the multi-contact connectors and thereby interconnects the circuit boards plugged into the connectors. It has been found to be useful in such an arrangement to use polarization keys which prevent a circuit board from being plugged into the wrong backplane connector by mistake. Such a polarization key is fitted at a selected location among the multiple contacts of a connector so that it will coincide with a gap or slot at the edge of the proper circuit board upon insertion. If the wrong circuit board is presented to the backplane connector, the key and gap will not coincide, thereby preventing the circuit board from being inserted.
One problem with a polarization key is the method of fastening it into the backplane connector, namely soldering the key to contacts of the connector. This is a procedure requiring some care. Moreover, if the key is ever to be moved, the contacts to which it was soldered are unfit for ordinary connector use.
Some conventional polarization keys have the drawback that they occupy more than one pair of backplane contacts, thereby eliminating additional contacts from electrical connector operation. It is an additional disadvantage of some conventional polarization keys that they are fabricated of plastic and are thereby too fragile for the use intended.
An additional disadvantage of conventional polarization keys arises from the particular environment in which they are used. For example, if it is desired to insert a circuit card into a backplane connector between two large circuit cards already installed, then the backplane connector may be virtually hidden from view before the insertion and completely hidden during the insertion. As a result, the insertion is carried out by feel. Conventional index keys often produce the result that the circuit card being inserted is blocked at a very small distance before the connector pads of the card engage the contacts of the backplane connector. In this circumstance, the person inserting the card may assume that he is encountering merely the insertion resistance of the mating connectors. Accordingly, he may push hard on the card being inserted and break the key or damage one or both of the connectors.